Method and apparatus for predicting semiconductor laser failure
First Claim
1. In a system comprising a semiconductor laser, an apparatus to predict failure of said semiconductor laser, said semiconductor laser being characterized by at least one of a current threshold, a slope efficiency and a dynamic resistance and outputting a light beam, the power in said light beam being a function of injection current input to said laser, said apparatus comprising:
- a photodetector configured to detect said power and output a corresponding power signal;
a modulating circuit configured to modulate said injection current with a predetermined modulation frequency and degree, said modulation frequency being selected so that operation of said system is not substantially disturbed by modulation in said power related to said modulated injection current; and
a processing circuit coupled to said photodetector and said laser for sampling said injection current and at least one of a laser voltage signal and said power signal while said modulating circuit modulates said injection current, the resulting samples forming a sample set;
said processing circuit being configured to extract from a multiplicity of said sample sets an updated laser characteristic which is a function of at least one of said current threshold, slope efficiency and dynamic resistance.
3 Assignments
0 Petitions
Accused Products
Abstract
A method and apparatus are disclosed for predicting the failure of semiconductor lasers. To predict the failure of a particular semiconductor laser, operational characteristics that are predictive of a laser'"'"'s health are computed while the laser is in use (e.g., while the laser is transmitting a signal or pumping an optical amplifier or solid state laser). This is done by modulating the injection current of the semiconductor laser and observing changes in laser parameters such as output power and junction voltage. From these observations, various laser characteristics can be computed including current threshold, slope efficiency and dynamic resistance. By carefully selecting the injection current modulation frequency and degree, the system in which the laser is used is not significantly disturbed by the changes in output power. For example, modulating the injection current with a modulation period that is substantially less than the relaxation time of the dopant ions in a solid-state laser does not substantially affect the gain of the solid state laser. The current modulation and laser parameter sampling are controlled by a microprocessor via a controller interface. During any particular modulation cycle, the microprocessor stores multiple parameter samples in a random access memory. Once enough samples have been stored, the microprocessor computes the laser characteristics and compares them to beginning-of-life data for the same semiconductor laser, which are stored in a read only memory. If the laser characteristics are out of range with respect to the beginning-of-life data, the microprocessor outputs an alarm via a serial interface.
-
Citations
21 Claims
-
1. In a system comprising a semiconductor laser, an apparatus to predict failure of said semiconductor laser, said semiconductor laser being characterized by at least one of a current threshold, a slope efficiency and a dynamic resistance and outputting a light beam, the power in said light beam being a function of injection current input to said laser, said apparatus comprising:
-
a photodetector configured to detect said power and output a corresponding power signal; a modulating circuit configured to modulate said injection current with a predetermined modulation frequency and degree, said modulation frequency being selected so that operation of said system is not substantially disturbed by modulation in said power related to said modulated injection current; and a processing circuit coupled to said photodetector and said laser for sampling said injection current and at least one of a laser voltage signal and said power signal while said modulating circuit modulates said injection current, the resulting samples forming a sample set; said processing circuit being configured to extract from a multiplicity of said sample sets an updated laser characteristic which is a function of at least one of said current threshold, slope efficiency and dynamic resistance.
-
-
2. In an optical amplifier configured to generate an amplified version of an input light signal using power in a pump light beam generated by a pump laser, an apparatus to predict failure of said pump laser, said apparatus consisting of:
-
a laser chip within said pump laser configured to output a first beam that becomes said pump light beam, said laser chip being characterized by a current threshold, a slope efficiency and a dynamic resistance, said laser chip outputting laser power, voltage and current signals while operating, the output power of said laser chip being controlled by said current signal; a computer coupled to said laser chip configured to control said current signal and receive said laser power, current and voltage signals;
said computer characterizing said pump laser by (1) causing the modulation of said current signal with a predetermined modulation frequency and degree about a desired operational current level, said modulation frequency being selected so that said amplified version is not substantially disturbed by said current modulation, (2) receiving multiple sets of said laser power, current and voltage signals while causing said current modulation, and (3) computing from said multiple sets an updated pump laser characteristic which is a function of at least one of said current threshold, slope efficiency and dynamic resistance. - View Dependent Claims (3, 4, 5)
-
-
6. A method for determining the health of a semiconductor laser comprising the steps of:
-
without disturbing operation of a system employing said semiconductor laser, modulating injection current of said laser with a predefined modulation period and degree around a desired operational current level; during said modulating, sampling operational parameters of said semiconductor laser including output power, junction voltage and said injection current to form a sample set; repeating said sampling step a predefined number of times, forming a multiplicity of sample sets; and from said multiplicity of sample sets, computing at least one operational health characteristic of said semiconductor laser which is a function of at least one of current threshold, slope efficiency, dynamic resistance and kinks. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
-
Specification